Helical baffle means in a tubular heat exchanger



Sept. 10, 1968 MAN SUK LEE 3,400,758

HELICAL BAFFLE MEANS IN A TUBULAR HEAT EXCHANGBR Filed May 16, 1966FIG-l INVENTOR. MAN SUK LEE HIS ATTO NEY United States Patent 3,400,758HELICAL BAFFLE MEANS IN A TUBULAR HEAT EXCHANGER Man Suk Lee, Dayton,Ohio, assignor to United Aircraft Products, Inc., Dayton, Ohio, acorporation of Ohio Filed May 16, 1966, Ser. No. 550,256 9 Claims. (Cl.165-459) ABSTRACT OF THE DISCLOSURE A tube and shell type heat exchangerwherein the shell side fluid is caused to flow over the tubes in ahelical path, baffle means being provided in the form of longitudinallyspaced segmental plate elements having flow control surfaces which areperpendicular to the axes of the tubes simplifying installation andremoval of the tubes.

This invention relates to tube and shell heat exchangers, that is, toheat exchangers comprised of a tube bundle installed in a shell for flowof a first fluid through the tubes and for flow of a second fluid overand around the tubes, the fluids being segregated and a transfer of heattaking place through the tube walls. Although not so limited, theinvention has special reference to compact forms of heat exchangershaving high density cores comprised of a large number of closely spacedapart tubes.

Tubular heat exchanger cores customarily incorporate baffles. These makepossible a maximum use of available pressure drop and are usuallyarranged to effect repeated crossing and re-crossing of the tube bundleby the described second fluid for optimum heat transfer effect. In thepast this has been done by installing in the tube bundle a series ofseparated, longitudinally spaced apart bafiles which enforce aserpentine flow of fluid over the tubes between shell openings definingan inlet and an outlet. Such a baffling arrangement has certaindisadvantages, as when portions of the provided heat transfer surfacemay be by-passed by the flowing fluid. More uniform flow at differentflow rates is possible in a helical flow path with possibly superiorheat transfer efficiency. However, the installing of battle means toobtain a helical flow has heretofore been impractical, particularly inhigh density cores.

The advantages of such a construction have not been seen to outweigh thedifficulties of fabrication, including the forming of the helix and theinstallation in the baffle means of large numbers of closely spacedtubes.

In accordance with the instant invention, however, generally new andimproved results are achieved with helical baffle means and problems offabrication are simplified or eliminated. The provision of a heatexchanger core having helical baflie means so characterized is an objectof the invention.

Another object of the invention is to provide helical baffle meanswherein openings in the baffles accommodating heat exchanger tubes arealigned for easy insertion and withdrawal of such tubes.

A further object of the invention is to construct a helical baflie meansas described with steps interposing restrictions in the path of movementof the flowing fluid over the tubes in such manner that the flowintermittently is restricted.

Still another object of the invention is to present a generally newbaffle means comprised of a plurality of component elements cooperatingwith one another to define a helix and being individually in a mutuallysupporting relation to tubes of the tube bundle.

Other objects and structural details of the invention will appear fromthe following description, when read "ice in connection with theaccompanying drawings, wherein:

FIG. 1 is a partly diagrammatic view of a tube and shell heat exchanger,the shell being shown in longitudinal section with the core therein inside elevation;

FIG. 2 is a fragmentary view in perspective of the core of FIG. 1, aportion of the core being exploded to show details of baflie elements;

FIG. 3 is a detail view of a series of related bafile elementscomprising the baffle means; and

FIG. 4 is a detail view of a modified form of baflle elements.

Referring to the drawings, a heat: exchanger in accordance with theinvention may comprise a shell 10 near respectively opposite ends ofwhich are bosses 11 and 12 respectively for the inlet and outlet of aflowing fluid. The ends of the shell are open for flow therethrough ofanother fluid. The two fluids achieve a segregated, heat transferrelation within the shell 10, the heat transfer surface being affordedby tubes 13. These have their ends mounted in header plates 14 and 15which are suitably perforated, as indicated at 16 in FIG. 2, to receiveand pass the tubes with a comparatively close fit. A large number ofclosely spaced apart openings 16 provide for a large number of tubes 13.For simplicity and clarity of illustration most of such openings are nothere shown, and only a few tubes 13 are shown.

The header plates 14 and 15 have a peripheral bearing in the shell 10and may be joined thereto in a leak proof manner. The fluid described asentering one end of the shell 10 and flowing longitudinally thereof toand through the opposite end is compelled to do so by flowing throughthe tubes 13. The fluid entering the shell 10 by way of inlet 11 andexiting by way of outlet 12 moves through the shell exteriorly of thetubes 13. The interior wall surface of the tubes 13 is thus contacted byone fluid of one temperature while the exterior wall surfaces of thetubes are contacted by another fluid at a different temperature. Heattransfer through the tube walls occurs, the fluid of higher temperatureyielding up some of its heat to the fluid of lower temperature. Asheretofore seen, in order to make optimal use of the heat transfersurface the fluid flowing exteriorly of the tubes is bafiied to moverepeatedly in a generally cross flow relation to the tubes. Suchbaflling is accomplished in accordance with the instant invention byhelical baflle means 16. Along with the tubes 13 and header plates 14and 15 the baffle means 16 comprises the core of the heat exchanger.conventionally the core is separately assembled and installed as a unitin the shell 10.

The baffle means 17 achieves its extended character by a succession ofangularly displaced steps. A perfect helix baflle is possible. Itpresents manufacturing difiiculties, however, and affords no means bywhich the holes to ac commodate the tubes 13 may be aligned insuccessive flights and may be round properly to receive the round tubes.Also, as will hereinafter more clearly appear, a perfect helix baifledoes not provide the intermittent flow restriction of the presentinvention. Accordingly, the baffle means 17 has a stepped configurationand includes in the main segmental lands 18 disposed to lie in planesperpendicular to the axes of the tubes 13.

Considering the baffle construction in greater detail, in theillustrated instance of FIGS. 1, 2 and 3, the baflie means is comprisedof a plurality of formed plate-like elements 19. Each element 19 iscomprised of a pair of lands 18 which may be considered as occupying aside-by-side relation offset in a longitudinal sense by a wall or ledge21 which unitarily joins the two lands at their adjacent edges. Oppositeedges of the respective lands have turned over extremities 22 whichproject oppositely of one another out of and at right angles to theplanes of their respective lands. The bent over extremities 22 of eachelement 19 are in a common plane and define what may be considered oneside edge of the element. The opposite side edge is defined by a curvedperiphery 23 conforming to and adapted substantially to seat against theinterior surface of the shell 10.

In assembling the baffle means, one of a pair of elements 19 insubstantially face to face relation is rotated to achieve the laterallyoffset reversely disposed position illustrated by the exploded elementsat the right hand end of FIG. 4. Moved in a relatively approachingdirection, corresponding turned over extremities 22 are caused tointerfit with one another and in limiting against respective lands 18interrupt such relative approaching motion. While a pair of elements 19is held so positioned, as for example by clamp means applied to theinterfitting extremities 22, other plate elements of appropriate rotarydisplacement are caused to approach and engage the assembled pair offrame elements at opposite ends thereof. The result is to extend thebaflle means and this action is continued until a baflle means ofdesired length is achieved. The assembly results in a continuous helixformed of angularly displaced lands 18 interconnected either by integralwalls 21 or by interfitting extremities 22 which are at right angles tothe walls 21 and serve the same purpose. Ledges 21 and interfittingextremities 22 provide steps longitudinally spacing the lands 18 ofindividual plate elements and of corresponding lands of adjacentelements. A helical flow path is formed having its entrance end at theinlet 11 and its exit at the outlet 12. The fluid in flowing throughsuch path has a swirling motion in generally cross flo'w relation to thetubes 13 and is conducted from the inlet 11 to the outlet 12 in a numberof turns appropriate to the heat rejection requirements, the allowedflow rates and pressure drops and other data pertinent to a particularheat exchanger.

In considering flow through the helical path as described it will beseen that the baffle construction intermittently enforces a flowrestriction where the ledges 21 of adjacent flights of the helix orwhere the interfitting bent over extremities 22 of adjacent flights arealigned with one another. A passage 24 (FIG. 1) is defined at theselocations of reduced cross sectional area as compared to the areaimmediately preceding and immediately beyond the such locations. Fluidencountering a passage 24 and an interposed step at the location of suchpassage has its flow constricted. The flow into the space beyond thepassage, which space may be considered an expansion chamber, occursunder increased velocity conditions producing random flow andturbulence. A higher heat transfer rate through the tube walls results.Additionally, in advance of the passage 24 the restricted fluid breaksup in the corner of the step, producing eddies and turbulence in amanner to obviate pools or locations of low flow.

The individual plate elements may be circular in form as shown in FIG.4, rather than semi-circular as in FIGS. 1 to 3. Thus, a plurality ofcircumferentially off-set lands 24 are positioned to occupy thequadrants of a circle. The circular configuration is split in one-halfportion of the element and extremities are bent over to define oppositeprojections 25 and 26. These correspond to the projections 22 of theplate elements 19 and are similarly adapted to interfit withcorresponding projecting portions of companion elements. The remaininglands or quadrants of the circular plate element are joined by integralconnecting walls 27 disposed at right angles to the lands 24 andachieving a longitudinally oflset relation of the several such lands.

The lands 18 and 24 may be described as defining surfaces, each bafflemeans providing a succession of longitudinally spaced, angularlydisplaced such surfaces.

It will be evident that other modifications in the instant heatexchanger structure are possible within the spirit and concept of theinvention as contained in the accompany- 4 ing drawings and in theforegoing description, and in accordance with the claims to follow.

What is claimed is:

1. A core for a tubulous heat exchanger, including a plurality of tubesarranged in a bundle of parallel tubes for flow through the tubes of afirst fluid and for flow over and around the tubes of a second fluid,heat transfer between the fluids occurring through the tube walls, andbaflle means in the form of longitudinally spaced baflle elements insaid tube bundle directing the flow of said second fluid, said baflleelements providing a succession of longitudinally spaced angularlydisplaced surfaces, said surfaces being interconnected at adjacent edgesand adjacent elements being interconnected to define a helix forming ahelical flow path for said second fluid, said surfaces being disposedsubstantially perpendicular to the longitudinal axes of said tubes andhaving openings receiving said tubes, said surfaces each conforming to aquadrant of a circle, the connected adjacent edges of said surfacesdefining walls disposed angularly of said surfaces.

2. A core for a tubulous heat exchanger, including a plurality of tubesarranged in a bundle of parallel tubes for flow through the tubes of afirst fluid and for flow over and around the tubes of a second fluid,heat transfer between the fluids occurring through the tube walls, andbaffle means in said tube bundle directing the flow of said secondfluid, said baflle means providing a succession of longitudinally spacedangularly displaced surfaces, said surfaces being interconnected atadjacent edges to define a helix forming a helical flow path for saidsecond fluid, said surfaces being disposed substantially perpendicularto the longitudinal axes of said tubes and having openings receivingsaid tubes, said baffle means being formed of plate-like elements, eachcomprised of a plurality of lands in offset parallel relation to oneanother and interconnected at adjacent edges by relatively angularlydisposed portions, other angularly disposed portions projectingoppositely from each element to achieve interengaging relation withcorresponding projecting portions of adjacent elements, said landsdefining said surfaces.

3. A core for a tubulous heat exchanger, including a plurality of tubesarranged in a bundle of parallel tubes for flow through the tubes of afirst fluid and for flow over and around the tubes of a second fluid,heat transfer between the fluids occurring through the tube walls, andbaflle means in said tube bundle directing the flow of said secondfluid, said batfle means providing a succession of longitudinally spacedangularly displaced surfaces, said surfaces being interconnected atadjacent edges to define a helix forming a helical flow path for saidsecond fluid, said surfaces being disposed substantially perpendicularto the longitudinal axes of said tubes and having openings receivingsaid tubes, said baffle means being formed of plate-like elements, eachcomprised of a succession of angularly displaced longitudinally spacedapart parallel lands, said lands defining said surfaces, said successionof lands terminating at its ends in portions projecting oppositely ofone another substantially at right angles to said lands whereby eachelement may be joined to adjacent elements to form continuing bafllemeans as described.

4. A core according to claim 3, characterized in that at least one ofsaid elements is circular in configuration providing four lands asdescribed defining the quadrants of a circle.

5. A core according to claim 3, characterized in that at least one ofsaid elements is semi-circular in configuration having two lands asdescribed in a side-by-side relation.

6. A core for a tubulous heat exchanger, including a plurality of tubesarranged in a bundle of parallel tubes for flow through the tubes of afirst fluid and for flow over and around the tubes of a second fluid,heat transfer between the fluids occurring through the tube walls,baffle means in said tube bundle directing the flow of said secondfluid, said baflie means providing a succession of longitudinally spacedangularly displaced surfaces, said surfaces being interconnected atadjacent edges to define a helix forming a helical flow path for saidsecond fluid, said surfaces being disposed substantially perpendicularto the longitudinal axis of said tubes and having openings receivingsaid tubes, .and steps in said baffle means resulting in longitudinallyspaced lands defining said surfaces, correspondingly positioned landsdefining a flow path therebetween, said flow path having on account ofsaid steps alternating portions of greater and lesser flow restriction.

7. A core for a tubulous heat exchanger, including a plurality of tubesarranged in a bundle of parallel tubes for flow through the tubes of afirst fluid and for flow over and around the tubes of a second fluid,heat transfer between the fluids occurring through the tube walls, andbalfle means in said tube bundle directing the flow of said secondfluid, said bafile means providing a succession of longitudinally spacedangularly displaced surfaces, said surfaces being interconnected atadjacent edges to define a helix forming a helical flow path for saidsecond fluid, said surfaces being disposed substantially perpendicularto the longitudinal axes of said tubes and having openings receivingsaid tubes, said baflle means being com prised of a helix made up of asuccession of lands parallel to one another to define said surfaces,adjoining lands being connected to one another along adjacent marginaledges by steps approximately at right angles to said lands, said stepsnarrowing said flow path at the locations thereof to provide foralternate restriction and expansion of the fluid flowing through saidpath.

8. A tubulous heat exchanger, including a cylindrical shell, perforateheader plates in spaced relation to one another in said shell, fluidflowing tubes extending between and opening through said header plates,inlet and outlet openings in said shell for flowing a fluid through saidshell over and around said tubes, and perforate baflie meansintermediate said inlet and outlet openings through which said tubesextend, said baflle means having the form of a helix having an outeredge substantially in contact with said shell and being comprised of asuccession of lands parallel to one another and approximately at rightangles to the axis of said shell, successive lands being angularlydisplaced from one another and interconnected by steps approximatelyparallel to the axis of said shell, said steps interposing restrictionsto flow in the helical flow path defined by said 'baflle means.

9. A tubulous heat exchanger according to claim 8, characterized in thatsaid baffle means is comprised of a succession of like elements, eachelement comprising a plurality of lands as described and terminating inportions of relatively opposite projection disposed approximately atright angles to said lands and cooperating with like portions onadjacent elements to define steps as described.

References Cited UNITED STATES PATENTS 1,335,506 3/1920 Jones l-16l1,469,193 9/1923 Sims 161 1,505,429 8/1924 Ripley 165--159 1,522,8661/1925 Colston 165161 1,764,200 6/1930 Dean 165-161 1,782,409 11/1930Chute 165-161 ROBERT A. OLEARY, Primary Examiner. A. W. DAVIS, AssistantExaminer,

